The present invention relates to an electromagnetic blower and a two-passage air supply apparatus using the same, and more particularly, to an electromagnetic blower with a simple, low-priced configuration, capable of singly changing its delivery of air in a multistage manner, and a two-passage air supply apparatus using the same.
As much importance has recently been attached to the problem of environmental health, septic tanks for purifying sewage, resources of water as one of surroundings, have been spreading. As shown in FIG. 9A, a septic tank 50 comprises a first settling-separating tank 51 and a second settling-separating tank 52 to be supplied with, e.g., sewage, a biological contact aeration tank 53 to be supplied with the sewage that is cleared of solid matter and the like in the settling-separating tanks 51 and 52, and a settling tank 54 for settling a mass (sludge) of microorganisms having purified the sewage in the biological contact aeration tank 53. Clear supernatant water in the settling tank 54 is disinfected and discharged through an outlet.
The biological contact aeration tank is provided with a contact filter medium 53a. Aerobic microbe on the surface of the contact filter medium 53a are propagated by aerating air that is fed from a first blower 61 through a pipe 62 and an air diffuser pipe 63, and decompose organisms in the sewage. In order to clean the contact filter medium 53a in the biological contact aeration tank, moreover, reverse cleaning air is loaded periodically or nonperiodically from a second blower 64 into the contact filter medium 53a through a pipe 65 and an air diffuser pipe 66 for a given short time of each day, for example.
In the conventional apparatus described above, however, the aerating air and the reverse cleaning air are supplied individually from the separate blowers, so that the two blowers are need and entail high cost. To cope with this problem, one blower is proposed singly to form aerating air and reverse cleaning air.
FIG. 9B shows one such blower. The configuration of a septic tank 50 in the drawing is identical with the one shown in FIG. 9A. In this apparatus, a blower 67 is connected to a three-way switching valve 68, and air discharged from the blower 67 is used as the aerating air, normally. When it is time for the reverse cleaning air to be supplied, the three-way switching valve 68 is switched so that the air discharged from the blower 67 serves as the reverse cleaning air for a given time.
As another prior art example, a valve 69 is provided in the middle of a path of supply for reverse cleaning air, as shown in FIG. 9C. When it is time for the reverse cleaning air to be supplied, the valve 69 is opened so that the air discharged from the blower 67 serves as the reverse cleaning air for a given time.
A technique related to the present invention is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-187496, for example. According to the technique described in this publication, first and second air compressors are arranged, and compressed air from the first air compressor is guided to first and second hoses through a three-way switching valve that is switched by means of compressed air from the second air compressor. By doing this, air is fed to the first hose to perform aeration, normally. When it is time for reverse cleaning to be started, the second air compressor is actuated to switch the three-way switching valve, and the compressed air from the first air compressor is connected to a hose for reverse cleaning.
According to the examples shown in FIGS. 9B and 9C, the aerating air and the reverse cleaning air can be formed by means of the single blower. Since the blower is always driven with its rated output (high output), however, there are problems of high-level noise from the blower and short life.
In the example shown in FIG. 9B, moreover, the pressure in the air diffuser pipe 63 for aeration is lower than the water pressure while the reverse cleaning air is being supplied to the contact filter medium 53a, so that water that contains sludge in the biological contact aeration tank 53 flows back into the air diffuser pipe 63 for aeration, thereby clogging the pipe. In the example shown in FIG. 9C, furthermore, air pressure for aeration is halved during reverse cleaning operation, so that air pressure for reverse cleaning is about half as high as the air pressure for aeration. Thus, the air pressure is low, and the efficiency of reverse cleaning is poor.
The object of the present invention is to provide a low-noise, long-life electromagnetic blower that is free from the above problems, has a simple, low-priced configuration, and can realize two different outputs, high and low.
In order to achieve the above object, according to the present invention, there is provided an electromagnetic blower including an electromagnet wound with a coil, a vibrator capable of being reciprocated by means of the magnetic force of the electromagnet generated by an alternating current supplied to the coil, and a diaphragm attached to an end portion of the vibrator, and designed so that compressed air is discharged as the diaphragm is actuated. The blower comprises switching means for allowing the alternating current to be supplied to only a part of the coil, and has a first feature in that a first mode in which the alternating current is supplied to the coil or a second mode in which the alternating current is supplied to only a part of the coil can be selected by controlling the switching means.
According to this feature, the electromagnetic blower can be operated with nonrated low output (aforesaid first mode) and rated high output (aforesaid second mode) with use of only the simple switching means. If the time for the operation with the low output is made longer than the time for the operation with the high output, the level of noise produced by the electromagnetic blower can be lowered, and the life of the electromagnetic blower can be lengthened.
Further, the present invention has a second feature in that the compressed air discharged from the electromagnetic blower is alternatively supplied to an air diffuser pipe for aeration for sewage purification and an air diffuser pipe for reverse cleaning through a switching pipe, that the electromagnetic blower is operated in the first mode during aeration and in the second mode during reverse cleaning operation, and that a throttle valve is connected between pipes for guiding the compressed air discharged from the electromagnetic blower to the air diffuser pipe for aeration and the air diffuser pipe for reverse cleaning.
According to this feature, the electromagnetic blower is operated with low output during aeration and with high output during reverse cleaning operation, so that it can operate with low noise during aeration, and its life can be lengthened. Since the throttle valve is connected between the pipes for guiding the compressed air to the air diffuser pipe for aeration and the air diffuser pipe for reverse cleaning, moreover, the internal pressure of the other air diffuser pipe cannot become lower than the water pressure while the compressed air is being supplied to one of the air diffuser pipes for aeration and reverse cleaning, so that sewage can be prevented from flowing back into the other air diffuser pipe. Thus, the air diffuser pipes can be prevented from being clogged with sewage.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.